Two-dimensional electron gas charge density control

ABSTRACT

Structures and related techniques for control of two-dimensional electron gas (2DEG) charge density in gallium nitride (GaN) devices are disclosed. In one aspect, a GaN device includes a compound semiconductor substrate, a source region formed in the compound semiconductor substrate, a drain region formed in the compound semiconductor substrate and separated from the source region, a 2DEG layer formed in the compound semiconductor substrate and extending between the source region and the drain region, a gate region formed on the compound semiconductor substrate and positioned between the source region and the drain region, and a plurality of isolated charge control structures disposed between the gate region and the drain region.

CROSS-REFERENCE TO RELATED APPLICATION

This present application claims the benefit of U.S. Provisionalapplication No. 63/213,655, filed on Jun. 22, 2021, entitled“TWO-DIMENSIONAL ELECTRON GAS CHARGE DENSITY CONTROL”, the entirecontents of which is incorporated herein by reference for all purposes.

FIELD

The described embodiments relate generally to compound semiconductordevices, and more particularly, the present embodiments relate totwo-dimensional electron gas charge density control in gallium nitride(GaN) devices.

BACKGROUND

In semiconductor technology, gallium nitride (GaN) is one compoundsemiconductor material that is used to form various devices, such ashigh power and/or high voltage transistors. These devices can be formedby growing epitaxial layers on silicon, silicon carbide, sapphire,gallium nitride, or other substrates. Often, such devices are formedusing a heteroepitaxial junction of aluminum gallium nitride (AlGaN) andGaN. This structure is known to form a high electron mobilitytwo-dimensional electron gas (2DEG) at the interface of the twomaterials. The electron gas can have a charge density in the 2DEG. Inmany applications, it may be desirable to control the charge density inthe 2DEG.

SUMMARY

In some embodiments, a gallium nitride (GaN) device is disclosed. TheGaN device includes a compound semiconductor substrate, a source regionformed in the compound semiconductor substrate, a drain region formed inthe compound semiconductor substrate and separated from the sourceregion, a two-dimensional electron gas (2DEG) layer formed in thecompound semiconductor substrate and extending between the source regionand the drain region, a gate region formed on the compound semiconductorsubstrate and positioned between the source region and the drain region,and a plurality of isolated charge control structures disposed betweenthe gate region and the drain region.

In some embodiments, each of the plurality of isolated charge controlstructures are arranged to selectively reduce a charge density in the2DEG layer under each of the plurality of isolated charge controlstructures.

In some embodiments, each of the plurality of isolated charge controlstructures is disposed on the compound semiconductor substrate.

In some embodiments, each of the plurality of isolated charge controlstructures includes a GaN layer.

In some embodiments, the GaN layer includes a P-type GaN layer.

In some embodiments, each of the plurality of isolated charge controlstructures is disposed within the compound semiconductor substrate.

In some embodiments, each of the plurality of isolated charge controlstructures includes an isolation implanted region.

In some embodiments, each of the plurality of isolated charge controlstructures includes an isolation implanted region formed through aP-type GaN layer.

In some embodiments, each of the plurality of isolated charge controlstructures are formed in shape of an island.

In some embodiments, the plurality of isolated charge control structuresare disposed proximal to the gate region.

In some embodiments, the plurality of isolated charge control structuresare arranged to reduce an electric field proximal to the gate region.

In some embodiments, a pattern density of the plurality of isolatedcharge control structures is constant in regions proximal to the gateregion and regions proximal to the drain region.

In some embodiments, each of the plurality of isolated charge controlstructures are formed in shape of a trapezoid extending from the gateregion towards the drain region.

In some embodiments, each of the plurality of isolated charge controlstructures are formed in shape of an ellipse extending from the gateregion towards the drain region.

In some embodiments, a method of controlling a charge density in atwo-dimensional electron gas (2DEG) layer in a gallium nitride (GaN)device is disclosed. The method includes providing a compoundsemiconductor substrate comprising a first layer and a second layer, andfurther comprising a 2DEG layer formed between the first layer and thesecond layer, forming an active region, forming a gate region on thecompound semiconductor substrate and across the active region, andforming a plurality of isolated charge control structures on the activeregion, where each of the plurality of isolated charge controlstructures are arranged to selectively reduce a charge density in the2DEG layer under each of the plurality of isolated charge controlstructures.

In some embodiments, in the disclosed method each of the plurality ofisolated charge control structures includes a P-type GaN layer.

In some embodiments, in the disclosed method each of the plurality ofisolated charge control structures includes an isolation implantedregion.

In some embodiments, gallium nitride (GaN) device is disclosed. The GaNdevice includes a compound semiconductor substrate, a two-dimensionalelectron gas (2DEG) layer formed in the compound semiconductorsubstrate, a resistor formed in the compound semiconductor substrate,the resistor comprising an active region, and a first and second ohmiccontacts, and a plurality of isolated charge control structures formedon at least a portion of the active region, where each of the pluralityof isolated charge control structures is arranged to reduce a chargedensity in the 2DEG layer under each of the plurality of isolated chargecontrol structures thereby causing an increase in a resistance of theresistor.

In some embodiments, each of the plurality of isolated charge controlstructures of the resistor includes a P-type GaN layer.

In some embodiments, a spacing between each adjacent charge controlstructure of the resistor is lower than a minimum manufacturing widthfor the active region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a side 3-D view of a GaN device using P-type GaNstructures to control 2DEG charge density according to an embodiment ofthe disclosure;

FIG. 1B shows a cross-sectional view of the GaN device of FIG. 1Aaccording to an embodiment of the disclosure;

FIG. 2A illustrates a side 3-D view of an embodiment of a GaN deviceusing isolation implant patterning according to an embodiment of thedisclosure;

FIG. 2B shows a cross-sectional view of GaN device of FIG. 2A accordingto an embodiment of the disclosure;

FIG. 3A illustrates a side 3-D view of an embodiment of a GaN deviceusing isolation implant through P-type GaN structures according to anembodiment of the disclosure;

FIG. 3B shows a cross-sectional view of GaN device of FIG. 3A accordingto an embodiment of the disclosure;

FIG. 4A illustrates a plan view of a GaN device according to anembodiment of the disclosure;

FIG. 4B shows 2DEG charge density as a function of location in the GaNdevice of FIG. 4A;

FIG. 5A illustrates a plan view of a GaN device according to anembodiment of the disclosure;

FIG. 5B shows 2DEG charge density as a function of location in the GaNdevice of FIG. 5A;

FIG. 6A illustrates a plan view of a GaN device according to anembodiment of the disclosure;

FIG. 6B shows 2DEG charge density as a function of location in the GaNdevice of FIG. 6A;

FIG. 7A illustrates a plan view of a GaN device according to anembodiment of the disclosure;

FIG. 7B shows 2DEG charge density as a function of location in the GaNdevice of FIG. 7A;

FIG. 8A illustrates a plan view of a GaN device according to anembodiment of the disclosure;

FIG. 8B shows 2DEG charge density as a function of location in the GaNdevice of FIG. 8A;

FIG. 9A illustrates a plan view of a GaN device according to anembodiment of the disclosure;

FIG. 9B shows 2DEG charge density as a function of location in the GaNdevice of FIG. 9A;

FIG. 10A illustrates various experimental test structures utilizing acharge control structure similar to FIG. 5A;

FIG. 10B shows C-V test results for the test structures of FIG. 10A;

FIG. 11A shows a cross-sectional view and a plan view of a GaNtransistor according to an embodiment of the disclosure;

FIG. 11B shows 2DEG charge density and electric field as a function oflocation along the active region for the GaN transistor of FIG. 11A;

FIG. 12A shows a cross-sectional view and a plan view of a GaNtransistor according to an embodiment of the disclosure;

FIG. 12B shows 2DEG charge density and electric field as a function oflocation along the active region for the GaN transistor of FIG. 12A;

FIG. 13A shows a cross-sectional view and a plan view of a GaNtransistor according to an embodiment of the disclosure;

FIG. 13B shows 2DEG charge density and electric field as a function oflocation along the active region for the GaN transistor of FIG. 13A;

FIG. 14 shows a plan view a GaN resistor according to an embodiment ofthe disclosure;

FIG. 15 shows a plan view a GaN resistor according to an embodiment ofthe disclosure; and

FIG. 16 shows a plan view a GaN resistor according to an embodiment ofthe disclosure;

FIG. 17 shows a cross-sectional view of a GaN device with P-type GaNislands and an additional AlGaN layer according to an embodiment of thedisclosure;

FIG. 18 shows a cross-sectional view of a GaN device with patternedisolation implantation and an additional AlGaN layer according to anembodiment of the disclosure; and

FIG. 19 shows a cross-sectional view of a GaN device with P-type GaNislands and patterned implantation, and an additional AlGaN layeraccording to an embodiment of the disclosure.

DETAILED DESCRIPTION

Structures and related techniques disclosed herein relate generally tocontrol of two-dimensional electron gas (2DEG) charge density in galliumnitride (GaN) devices. More specifically, devices, structures andrelated techniques disclosed herein relate to GaN transistors whereP-type GaN structures, isolation implant patterning, and isolationimplantation through P-type GaN structures can be utilized to control2DEG charge density. In various embodiments, the 2DEG charge densitycontrol can enable modification of the transistor threshold voltage(Vth), and/or lowering of output capacitance of the transistor enablingrelatively high operating frequency. In some embodiments, the control of2DEG charge density can enable a reduction in the size of the GaNtransistor. In various embodiments, the control of the 2DEG chargedensity can enable fabrication of relatively high value 2DEG resistorsin same area, thus enabling a reduction in overall die area. Variousinventive embodiments are described herein, including methods,processes, systems, devices, and the like.

Several illustrative embodiments will now be described with respect tothe accompanying drawings, which form a part hereof. The ensuingdescription provides embodiment(s) only and is not intended to limit thescope, applicability, or configuration of the disclosure. Rather, theensuing description of the embodiment(s) will provide those skilled inthe art with an enabling description for implementing one or moreembodiments. It is understood that various changes may be made in thefunction and arrangement of elements without departing from the spiritand scope of this disclosure. In the following description, for thepurposes of explanation, specific details are set forth in order toprovide a thorough understanding of certain inventive embodiments.However, it will be apparent that various embodiments may be practicedwithout these specific details. The figures and description are notintended to be restrictive. The word “example” or “exemplary” is usedherein to mean “serving as an example, instance, or illustration.” Anyembodiment or design described herein as “exemplary” or “example” is notnecessarily to be construed as preferred or advantageous over otherembodiments or designs.

FIG. 1A illustrates an isometric view of a GaN device 100A using P-typeGaN structures to control 2DEG charge density according to an embodimentof the disclosure. As shown in FIG. 1A, the GaN device 100A can includea GaN layer 104, an AlGaN layer 108 and a 2DEG layer 106 formed betweenthe GaN layer and the AlGaN layer. In some embodiments, P-type GaNislands 102 can be added to the device 100A where the P-type GaN islandsare disposed on the AlGaN layer 108. The P-type GaN islands 102 candeplete charge carriers and reduce charge density in the 2DEG layer 106.The amount of 2DEG charge density reduction can depend on area 112 andspacing 110 of the P-type GaN islands 102 (discussed in more detail inFIG. 1B). Patterning of P-type GaN islands 102 can provide 2DEG chargedensity control without a need to change fabrication processes which canentail costly and complex fabrication process changes.

FIG. 1B illustrates a cross-sectional view 100B of GaN device 100A shownin FIG. 1A. As shown in FIG. 1B, the charge density in 2DEG layer 106can be reduced under the P-type GaN islands 102 (for example location116) compared to regions where there are no P-type GaN islands (forexample location 114). The amount of 2DEG charge density reduction candepend on area 112 (see FIG. 1A) and spacing 110 of the P-type GaNislands 102. In some embodiments, area 112 of each island 102 can be,for example, 1.0 um² while spacing 110 between each island can be 1.0um. In various embodiments, area 112 of islands 102 can be 1.5 um² witha spacing 110 of 1.5 um, while in other embodiments the area can bebetween 0.5 and 2.0 um² with a spacing between 0.5 to 2.0 um, and in yetother embodiments the area can be between 0.2 and 5.0 um² with a spacingbetween 0.2 to 5.0 um. As appreciated by one of ordinary skill in theart having the benefit of this disclosure, the area 112 and spacing 110of the islands 102 can be set to any suitable value. Further, asappreciated by one of ordinary skill in the art, the 2DEG charge densitytechnique described above can employ one or more islands, differentsizes and shapes for each island, non-uniform spacing between eachisland and other characteristics that can be different than thosedescribed herein. Moreover, as appreciated by one of ordinary skill inthe art, the P-type GaN layer can have varying values of dopingdensities.

In order to better appreciate the features and aspects of 2DEG chargecontrol structures and techniques for GaN devices according to thepresent disclosure, further context for the disclosure is provided inthe following section by discussing several particular implementationsof charge control structures for GaN devices according to embodiments ofthe present disclosure. These embodiments are for example only and otherembodiments can be employed in other compound semiconductor devices suchas, but not limited to any high electron mobility transistors (HEMT).

FIG. 2A illustrates an isometric view of an embodiment of GaN device200A using isolation implant patterning to control 2DEG charge densityaccording to an embodiment of the disclosure. As shown in FIG. 2A, theGaN device 200A can include a GaN layer 204, an AlGaN layer 208 and a2DEG layer 206 formed between the GaN layer and the AlGaN layer. In someembodiments, isolation implant regions 202 can be utilized in the GaNdevice 200A where an isolation implant can be placed into the activeregions of the GaN device. The isolation implant regions 202 can producedamaged lattice structure in the underlying AlGaN layer 208 and GaNlayer 204, eliminating charge carriers in the 2DEG layer 206. Further,the damaged lattice structures can reduce piezoelectric effects beyondthe immediate implanted regions and can cause a reduction of chargecarriers in the adjacent 2DEG regions (further discussed in FIG. 2B). Insome embodiments, the amount of 2DEG charge density reduction can dependon area 212 and spacing 210 of the isolation implant regions 202(discussed further in FIG. 2B).

FIG. 2B shows a cross-sectional view 200B of GaN device 200A shown inFIG. 2A. In some embodiments, the 2DEG charge carriers can be eliminatedwhere the isolation implant regions 202 are placed because the isolationimplant can penetrate through the AlGaN layer 208 and at least partiallythrough the GaN layer 204 and can damage the lattice structure. Further,damaged lattice structures can cause reduced piezoelectric effectsbeyond the immediate implanted regions and can cause a reduction ofcharge carriers in adjacent regions 220. The amount of 2DEG chargedensity reduction can depend on area 212 and spacing 210 of the implantregions 202. An area 212 of implant region 202 can be, for example, 1.0um² while a spacing 210 between implant regions can be 1.0 um. In someembodiments an area 212 of implant regions 202 can be 1.5 um² with aspacing 210 of 1.5 um, while in other embodiments the area can bebetween 0.5 and 2.0 um² with a spacing between 0.5 to 2.0 um, and invarious embodiments the area can be between 0.2 and 5.0 um² with aspacing between 0.2 to 5.0 um. As appreciated by one of ordinary skillin the art having the benefit of this disclosure, the area and spacingof implant regions 202 can be set to any suitable value. Further, asappreciated by one of ordinary skill in the art, the disclosed techniqueto modify the 2DEG charge density can include one or more implantregions 202, different sizes and shape of implant regions and othercharacteristics that can be different than those described herein.Moreover, as appreciated by one of ordinary skill in the art, theisolation dose and implant energy can have any suitable values.

FIG. 3A illustrates an isometric view of an embodiment of GaN device300A using isolation implanted regions through P-type GaN structures,according to an embodiment of the disclosure. In the illustratedembodiment, isolation implanted regions 302 through P-type GaNstructures 320 can be utilized to control charge density in 2DEG layer306 of the GaN device 300A. As shown in FIG. 3A, the GaN device 300A caninclude a GaN layer 304, an AlGaN layer 308 and a 2DEG layer 306 formedbetween the GaN layer and the AlGaN layer. In some embodiments,isolation implanted regions 302 can be formed by implanting thoughP-type GaN structures 320. The isolation implanted regions 302 can beutilized in active regions of GaN device 300A to reduce the chargedensity in the 2DEG layer 306. In the illustrated embodiment, due topresence of P-type GaN structures 320, the isolation implanted regions302 can penetrate less into the substrate, thus the produced latticestructure damage may not completely eliminate the charge carriers in the2DEG layer 306. The amount of 2DEG charge density reduction can dependon area 312 and spacing 310 of the isolation implanted regions 302(discussed further in FIG. 2B).

FIG. 3B shows a cross-sectional view 300B of GaN device 300A. In FIG.3B, GaN layer 304, AlGaN layer 308, and 2DEG layer 306 are shown.Regions of reduced 2DEG charge density 324 in 2DEG layer 306 are alignedwith isolation implanted regions 302 and regions of increased chargedensity 322 in 2DEG layer are positioned in between isolation implantedregions. The charge carriers in 2DEG layer 306 can be reduced where theisolation implanted regions 302 are placed because the isolation implantthrough P-type GaN structure 320 can penetrate through the AlGaN layer308 and damage the lattice structure, however in this embodimentisolation implantation may penetrate into the GaN layer but not as deepas direct implantation on AlGaN surface. Less penetration can lower theimplantation-based strain reduction compared to the direct implantationon AlGaN surface. In this way, the isolation implanted regions 302 cancause a reduction of carrier charges in the 2DEG layer 306 proximate theisolation implanted regions 302, but do not cause a complete eliminationof the carriers.

The amount of 2DEG charge density reduction can depend on area 312 (seeFIG. 3A) and spacing 310 of the isolation implanted regions 302. An area312 of isolation implanted regions 302 can be, for example, 1.0 um²while a spacing 310 between isolation implanted regions can be 1.0 um.In some embodiments an area 312 of isolation implanted regions 302 canbe 1.5 um² with a spacing 310 of 1.5 um, while in other embodiments thearea can be between 0.5 and 2.0 um² with a spacing between 0.5 to 2.0um, and in various embodiments the area can be between 0.2 and 5.0 um²with a spacing between 0.2 to 5.0 um. As appreciated by one of ordinaryskill in the art having the benefit of this disclosure, the area 312 andspacing 310 of isolation implanted regions 302 can be set to anysuitable values. Further, as appreciated by one of ordinary skill in theart, disclosed 2DEG charge density modification technique disclosedabove can include one or more isolation implanted regions, differentsizes and shapes for isolation implanted regions and othercharacteristics that can be different than those described herein.Moreover, as appreciated by one of ordinary skill in the art, theisolation dose and implant energy can have any suitable values.

FIG. 4A illustrates a plan view of GaN device 400A according to anembodiment of the disclosure. GaN device 400A can include a gate 402 andan active region 406, where 2DEG charge control structures 404 have beenadded to the active region. Charge control structures 404 can have areas408 and spacings 410. Charge control structures may be formed in shapeof islands. Value of the areas 408 and spacings 410 may vary. In someembodiments structures 404 can be P-type GaN structures similar todevice 100A, while in other embodiments they can be isolation implantregions similar to device 200A and in various embodiments they can beisolation implanted regions through P-type GaN structures similar todevice 300A. The area 408, spacing 410 and the number of structures 404can be used to control 2DEG charge density as shown in FIG. 400B. In theillustrated embodiment, a density of the islands can be constant inregions proximal and distal to the gate 402.

As illustrated in FIG. 4B, graph 400B shows a first plot 422 of 2DEGcharge density as a function of location in the active region 406 withcharge control structures 404, while second plot 420 shows the chargedensity without charge control structures 404 (for reference). As can beseen in plot 422, the charge density is reduced where structures 404 arepresent, and is increased in regions without structures 404. Area 408 ofstructures 404 can be, for example, 1.0 um² while a spacing 410 betweenstructures 404 can be 1.0 um. In some embodiments the area 408 can be1.5 um² with a spacing 410 of 1.5 um, while in other embodiments thearea can be between 0.5 and 2.0 um² with a spacing between 0.5 to 2.0um, and in various embodiments the area can be between 0.2 and 5.0 um²with a spacing between 0.2 to 5.0 um. As appreciated by one of ordinaryskill in the art having the benefit of this disclosure, the area 408 andspacing 410 of the structures 404 can be set to any suitable value.Further, as appreciated by one of ordinary skill in the art, structures404 can have different sizes and shapes, for example, but not limitedto, square, rectangular, circular, triangular, or trapezoid and can haveother characteristics that can be different than those described here.

FIG. 5A illustrates a plan view of GaN device 500A according to anembodiment of the disclosure. GaN device 500A can include a gate 502 andan active region 506, where 2DEG charge control structures 504 have beenadded to the active region. Structures 504 can have areas 508 andspacings 510 that can vary. Structures 504 can be P-type GaN structuressimilar to device 100A, isolation implant regions similar to device 200Aor isolation implant regions through P-type GaN structures similar todevice 300A. The area 508, spacing 510 and the number of structures 504can be used to control 2DEG charge density as shown in FIG. 5B. Asillustrated in FIG. 5B, graph 500B shows 2DEG charge density as afunction of location in the active region. First plot 522 shows 2DEGcharge density with structures 504, while plot 520 shows 2DEG chargedensity without structures 504. In the illustrated embodiment, a densityof charge control structures (islands) may decrease in regions proximalthe gate 502 and increase in regions distal to the gate 502.

As can be seen in graph 500B, the charge density is reduced wherestructures 504 are present, and is increased in regions withoutstructures 504. In regions proximal to the gate 502, there is a lowerdensity of structures 504, which can result a higher charge density inthose regions. Area 508 of structures 504 can be, for example, 1.0 um²while a spacing 510 between structures 504 can be 1.0 um. In someembodiments, area 508 can be 1.5 um² with a spacing 510 of 1.5 um, whilein other embodiments the area can be between 0.5 and 2.0 um² with aspacing between 0.5 to 2.0 um, and in various embodiments the area canbe between 0.2 and 5.0 um² with a spacing between 0.2 to 5.0 um. Asappreciated by one of ordinary skill in the art having the benefit ofthis disclosure, the area 508 and spacing 510 of the structures 504 canbe set to any suitable value. Further, as appreciated by one of ordinaryskill in the art, structures 504 can have different sizes and shapes,for example, but not limited to, square, rectangular, circular,triangular, or trapezoid and can have other characteristics that can bedifferent than those described here.

FIG. 6A illustrates a plan view of GaN device 600A according to anembodiment of the disclosure. GaN device 600A can include a gate 602 andan active region 606, where 2DEG charge control structures 604 have beenadded to the active region. Structures 604 can have areas 608 andspacings 610 that can vary. Structures 604 can be P-type GaN structuressimilar to device 100A, isolation implant regions similar to device 200Aor isolation implant regions through P-type GaN structures similar todevice 300A. The area 608, spacing 610 and the number of structures 604can be used to control 2DEG charge density as shown in FIG. 6B. Asillustrated in FIG. 6B, graph 600B shows 2DEG charge density as afunction of location in the active region. First plot 622 shows 2DEGcharge density with structures 604, while second plot 620 shows 2DEGcharge density without structures 604. In the illustrated embodiment, adensity of the charge control structures (islands) may be constant inregions proximal the gate 602 and decrease in regions distal to the gate602.

As can be seen in first plot 622, the 2DEG charge density is reducedwhere structures 604 are present, and is increased in regions withoutstructures 604. In regions of active region 606 that are away from thegate 602, there is a lower density of structures 604, which can resultin a higher charge density in those regions. Area 608 of structures 604can be, for example, 1.0 um² while a spacing 610 between structures 604can be 1.0 um. In some embodiments the area 608 can be 1.5 um² with aspacing 610 of 1.5 um, while in other embodiments the area can bebetween 0.5 and 2.0 um² with a spacing between 0.5 to 2.0 um, and invarious embodiments the area can be between 0.2 and 5.0 um² with aspacing between 0.2 to 5.0 um. As appreciated by one of ordinary skillin the art having the benefit of this disclosure, the area 608 andspacing 610 of the structures 604 can be set to any suitable value.Further, as appreciated by one of ordinary skill in the art, structures604 can have different sizes and shapes, for example, but not limitedto, square, rectangular, circular, triangular, or trapezoid and can haveother characteristics that can be different than those described here.

FIG. 7A illustrates a plan view of GaN device 700A according to anembodiment of the disclosure. GaN device 700A can include a gate 702 andan active region 706, where 2DEG charge control structures 704 have beenadded to the active region. Structures 704 can have areas 708 andspacings 710 that can vary. Structures 704 can be P-type GaN structuressimilar to device 100A, isolation implant regions similar to device 200Aor isolation implant regions through P-type GaN structures similar todevice 300A. The area 708, spacing 710 and the number of structures 704can be used to control 2DEG charge density as shown in FIG. 700B. Asillustrated in FIG. 7B, graph 700B shows 2DEG charge density as afunction of location in the active region 706. First plot 722 shows the2DEG charge density with structures 704, while second plot 720 shows the2DEG charge density without structures 704. In the illustratedembodiment, a density of the charge control structures (islands) maydecrease in regions proximal the gate 702, increase and decrease inregions distal to the gate 702.

As can be seen in graph 700B, the charge density is reduced wherestructures 704 are present, and is increased in regions withoutstructures 704. In regions proximate and away from the gate 702, thereis a lower density of 704, which can result in a higher charge densityin those regions. Area 708 of structures 704 can be, for example, 1.0um² while a spacing 710 between structures 704 can be 1.0 um. In someembodiments the area 708 can be 1.5 um² with a spacing 710 of 1.5 um,while in other embodiments the area can be between 0.5 and 2.0 um² witha spacing between 0.5 to 2.0 um, and in various embodiments the area canbe between 0.2 and 5.0 um² with a spacing between 0.2 to 5.0 um. Asappreciated by one of ordinary skill in the art having the benefit ofthis disclosure, the area 708 and spacing 710 of the structures 704 canbe set to any suitable value. Further, as appreciated by one of ordinaryskill in the art, structures 704 can have different sizes and shapes,for example, but not limited to, square, rectangular, circular,triangular, or trapezoid and can have other characteristics that can bedifferent than those described here.

FIG. 8A illustrates a plan view of GaN device 800A according to anembodiment of the disclosure. GaN device 800A can include a gate 802 andan active region 806, where 2DEG charge control structures 804 have beenadded to the active region. Structures 804 can have areas 808 andspacings 810 that can vary. Structures 804 can be P-type GaN structuressimilar to device 100A, isolation implant regions similar to device 200Aor isolation implant regions through P-type GaN structures similar todevice 300A. The area 808, spacing 810 and the number of structures 804can be used to control 2DEG charge density as shown in FIG. 8B. Asillustrated in FIG. 8B, graph 800B shows 2DEG charge density as afunction of location in the active region 806. First plot 822 showscharge density in the 2DEG region with structures 804, while second plot820 shows charge density without structures 804. In the illustratedembodiment, a density of the charge control structures (islands) may beconstant in regions proximal the gate 802, decrease and increase inregions distal to the gate 802.

As can be seen in first plot 822, the charge density is reduced wherestructures 804 are present, and is increased in regions withoutstructures 804. In regions where there is a lower density of structures804 the charge density can be higher than regions that have a higherdensity of structures 804. Area 808 of structures 804 can be, forexample, 1.0 um² while a spacing 810 between structures 804 can be 1.0um. In some embodiments the area 808 can be 1.5 um² with a spacing 810of 1.5 um, while in other embodiments the area can be between 0.5 and2.0 um² with a spacing between 0.5 to 2.0 um, and in various embodimentsthe area can be between 0.2 and 5.0 um² with a spacing between 0.2 to5.0 um. As appreciated by one of ordinary skill in the art having thebenefit of this disclosure, the area and spacing of the structures canbe set to any suitable value. Further, as appreciated by one of ordinaryskill in the art, structures 804 can have different sizes and shapes,for example, but not limited to, square, rectangular, circular,triangular, or trapezoid and can have other characteristics that can bedifferent than those described here.

FIG. 9A illustrates a plan view of GaN device 900A according to anembodiment of the disclosure. GaN device 900A can include a gate 902 andan active region 906, where 2DEG charge control structures 904 have beenadded to the active region. Structures 904 can have areas 908 andspacings 910 that can vary. Structures 904 can be P-type GaN structuressimilar to device 100A, isolation implant regions similar to device 200Aor isolation implant regions through P-type GaN structures similar todevice 300A. The area 908, spacing 910 and the number of structures 904can be used to control 2DEG charge density as shown in FIG. 900B. Asillustrated in FIG. 9B, graph 900B shows 2DEG charge density as afunction of location in the active region 906. First plot 922 showscharge density in the 2DEG layer with structures 904, while second plot920 shows charge density without structures 904.

As can be seen in FIGS. 9A and 9B, the charge density is reduced wherestructures 904 are present, and is increased in regions withoutstructures 904. In regions where there is a lower density of structures904 the charge density can be higher while in regions having a higherdensity of structures the charge density can be relatively lower. Area908 of structures 904 can be, for example, 1.0 um² while a spacing 910between structures 904 can be 1.0 um. In some embodiments the area 908can be 1.5 um² with a spacing 910 of 1.5 um, while in other embodimentsthe area can be between 0.5 and 2.0 um² with a spacing between 0.5 to2.0 um, and in various embodiments the area can be between 0.2 and 5.0um² with a spacing between 0.2 to 5.0 um. As appreciated by one ofordinary skill in the art having the benefit of this disclosure, thearea 908 and spacing 910 of the structures 904 can be set to anysuitable value. Further, as appreciated by one of ordinary skill in theart, structures 904 can have different sizes and shapes, for example,but not limited to, square, rectangular, circular, triangular, ortrapezoid and can have other characteristics that can be different thanthose described here.

FIG. 10A illustrates a series of charge density modification coupons1000A utilizing 2DEG charge control structures similar to the chargecontrol structures of FIG. 5A. Coupon 1002 is a reference transistorwhile coupons 1004, 1006, 1008 and 1010 are transistors with varyingsizes and spacings for the charge control structures in their activeregion. FIG. 10B shows C-V test results 1000B for the coupons of FIG.10A. In FIG. 10B, capacitance as a function of gate to source voltage(Vgs) is plotted for each of the coupons in FIG. 10A. As can be seen inthe C-V plots of FIG. 10B, the arrangement of the charge controlstructures can be used to control charge density in the coupons becausethe threshold voltage shifts for each of the coupons 1004 to 1010compared to the threshold voltage of coupon 1002. Further, as size ofthe charge control structures increases, charge density is reduced.Similarly, as spacing between the charge control structures is reducedthe charge density is reduced as well. This reduction in charge densitycan reduce output capacitance of the transistor and can enable increasedswitching frequency of the transistor.

FIG. 11A shows a cross-sectional view and a plan view of a GaNtransistor 1100A according to an embodiment of the disclosure. In FIG.11A, a cross-sectional view of GaN transistor with a source region 1104,gate region 1102, drift region 1106, drain region 1108 and a 2DEG layer1122 is shown. A plan view of a zoomed-in section 1120 is also shown,where gate 1110, active region 1112 and charge controlled regions 1114are shown. The charge control regions have a staircase trapezoidalshape. The charge controlled regions 1114 can be P-type GaN, isolationimplant regions and/or a combination of the P-type GaN and isolationimplant structures. FIG. 11B shows 2DEG charge density and electricfield as a function of location along the active region for the GaNtransistor 1100A. As shown in FIG. 11B, 2DEG charge density 1127 isreduced proximate to the gate region 1102 due to the presence of thecharge controlled regions 1114. As a result of reduced charge density,electric field 1125 is reduced in the region proximate the gate region1102 compared to the electric field for a case without charge controlstructures (1129). In various embodiments, reduction of 2DEG chargedensity proximal to the gate of the transistor can enable reduction ingate length, and can enable a reduction in die area. As appreciated byone of ordinary skill in the art having the benefit of this disclosure,charge control structures can be continuous structure and/or can be inshape of islands. Further, as appreciated by one of ordinary skill inthe art, charge control structures can have varying sizes and spacings.

FIG. 12A shows a cross-sectional view and a plan view of a GaNtransistor 1200A according to an embodiment of the disclosure. In FIG.12A, a cross-sectional view of GaN transistor 1200A with a source region1204, gate region 1202, drift region 1206, drain region 1208 and a 2DEGlayer 1222 is shown. A plan view of a zoomed-in section 1220 is alsoshown, where gate 1210, active region 1212 and charge controlled regions1214 are shown. In this embodiment the charge controlled regions 1214have a triangular or a trapezoidal shapes. The charge controlled regions1214 can be P-type GaN, isolation implant and/or a combination of theP-type GaN and isolation implant structures. FIG. 12B shows 2DEG chargedensity and electric field as a function of location along the activeregion. As shown in FIG. 12B, 2DEG charge density 1227 is reducedproximate the gate region 1202 due to the presence of the chargecontrolled regions 1214. As a result of reduced charge density, electricfield 1225 is reduced in a region proximate the gate region 1202compared to the electric field for a case without charge controlstructures (1229). As appreciated by one of ordinary skill in the arthaving the benefit of this disclosure, charge control structures can becontinuous structure and/or can be in shape of islands. Further, asappreciated by one of ordinary skill in the art, charge controlstructures can have varying sizes and spacings.

FIG. 13A shows a cross-sectional view and a plan view of a GaNtransistor 1300A according to an embodiment of the disclosure. In FIG.13A, a cross-sectional view of GaN transistor with a source region 1304,gate region 1302, drift region 1306, drain region 1308 and a 2DEG layer1322 is shown. A plan view of a zoomed-in section 1320 is also shown,where gate 1310, active region 1312 and charge controlled regions 1314are shown. In this embodiment the charge control regions have anellipsoidal shape. The charge control regions can be P-type GaN,isolation implant and/or a combination of the P-type GaN and isolationimplant structures. FIG. 13B shows 2DEG charge density and electricfield as a function of location along the active region. As shown inFIG. 13B, 2DEG charge density 1327 is reduced proximate the gate region1302 due to the presence of the charge controlled regions 1314. As aresult of reduced charge density, electric field 1325 is reduced in aregion proximate the gate region 1302 compared to the electric field fora case without charge control structures (1329). As appreciated by oneof ordinary skill in the art having the benefit of this disclosure,charge control structures can be continuous structure and/or can be inshape of islands. Further, as appreciated by one of ordinary skill inthe art, charge control structures can have varying sizes and spacings.

FIG. 14 shows a plan view of a GaN resistor 1400 according to anembodiment of the disclosure. GaN resistor 1400 can include ohmiccontact regions 1402, active region 1408, and isolation implantedregions 1404. In some embodiments the ohmic contact regions 1402 can bemetallic contact regions. The active region 1408, which in thisembodiment has a dog-bone shape, can enable formation of a 2DEG in thesubstrate, where a resistance value of the resistor can be set by aminimum manufacturing active region width 1412. A width of the minimummanufacturing active region width 1412 may be set by a minimummanufacturing spacing between the implanted regions 1404. In theillustrated embodiment, P-type GaN charge control structures 1406 can beadded to the resistor in order to form a relatively high value resistor.The charge control structures can have a minimum manufacturing spacing1410. A value of spacing 1410 can be lower than active region width1412, thus enabling formation of a relatively high value resistor. Inthis way, manufacturing limitations on minimum spacing of implantedregions can be circumvented. Furthermore, this technique can allow theformation of relatively high value resistors without a need for costlyand complex change in manufacturing equipment. Furthermore, the use ofP-type GaN charge control structures can enable improved manufacturingcontrol of the resistor value as compared to a resistor formed withoutcharge control structures. For example, if a minimum manufacturingdesign rule is set at 10 nm for an active width, this technique canenable manufacturing of a resistor having a resistance value that can beequal to a resistance of a resistor having an active width of 8 nm. Asappreciated by one of ordinary skill in the art having the benefit ofthis disclosure, the minimum manufacturing design rule for an activewidth and spacing can vary for various semiconductor manufacturingprocesses.

FIG. 15 shows a plan view of a GaN resistor 1500 according to anembodiment of the disclosure. GaN resistor 1500 can include ohmiccontact regions 1502, active region 1508, and isolation implantedregions 1504. In some embodiments the ohmic contact regions 1502 can bemetallic contact regions. In the illustrated embodiment, the activeregion 1508 having a shape of a rectangle, can have a non-minimummanufacturing width of 1512. As understood by those skilled in the art,a non-minimum manufacturing feature size is a feature size which doesnot use a minimum feature size of the manufacturing process. P-type GaNcharge control structures 1506 can be added to the resistor in order toform a relatively high value resistor. The charge control structures canhave a minimum manufacturing spacing 1510. Thus, a relatively high valueresistor can be formed even with a non-minimum width of the activeregion. Furthermore, the use of P-type GaN charge control structures canenable improved manufacturing controls in the value of the resistor ascompared to a resistor formed without the charge control structure.

FIG. 16 shows a plan view of a GaN resistor 1600 according to anembodiment of the disclosure. GaN resistor 1600 can include ohmiccontact regions 1602, active region 1608, and isolation implantedregions 1604. In some embodiments the ohmic contact regions can bemetallic contact regions. The active region, which can have dog-boneshape, can enable formation of 2DEG in the substrate, where a value ofthe resistor can be determined by a minimum manufacturing width of theactive region 1612. A width of the minimum active region width 1612 maybe set by a minimum manufacturing spacing between the implanted regions1604. In the illustrated embodiment, P-type GaN charge controlstructures 1606 can be added to the resistor in order to form arelatively high value resistor. The P-type GaN structure can be in formof multiple islands. The charge control structures can have a minimummanufacturing spacing 1610. In some embodiments, spacing 1610 can beless than the minimum active region width 1612, thus enabling formationof a relatively high value resistor. In this way, manufacturinglimitations on minimum spacing of implanted regions can be circumvented,and this technique can allow the formation of relatively high valueresistors without a need for costly and complex changes in manufacturingequipment. Furthermore, the use of P-type GaN charge control structurescan enable improved manufacturing control of the resistor value ascompared to a resistor formed without charge control structures.

FIG. 17 illustrates a cross-sectional view of GaN device 1700. The GaNdevice 1700 can include a GaN layer 1704, a first AlGaN layer 1708, anda 2DEG layer 1706 formed between the GaN layer 1704 and the first AlGaNlayer 1708. The GaN device 1700 can also include islands 1702. In someembodiments, the islands 1702 can be formed from P-type GaN material.The GaN device 1700 can further include a second AlGaN layer 1705 formedon the first AlGaN layer 1708. In the illustrated embodiment, the secondAlGaN layer 1705 can be removed in some areas, such as in area 1720. Asdiscussed above, the 2DEG charge density can be reduced under the P-typeGaN islands 1702 (for example, location 1716) compared to regions withno P-type GaN islands (for example location 1714). The addition ofsecond AlGaN layer 1705 on the first AlGaN layer 1708 in the area 1722can increase the charge density in the 2DEG layer 1706 below the secondAlGaN layer 1705 (for example location 1718). As before, the presence ofP-type GaN islands in area 1722 can decrease the 2DEG charge densitybelow the islands, for example, location 1712, however the 2DEG chargedensity in location 1712 can be higher than the 2DEG charge density inlocation 1716, due to the presence of the second AlGaN layer 1705 overthe location 1712. Thus, this method can allow for control of the 2DEGcharge density in various locations in a GaN substrate and/or GaN wafer.

An amount of 2DEG charge density increase due to presence of the secondAlGaN layer 1705 can depend on a thickness of the second AlGaN layer1705. In some embodiments, the thickness of the second AlGaN layer 1705can be, for example, 50 nm. In various embodiments, the thickness of thesecond AlGaN layer 1705 can be, for example, 100 nm, while in otherembodiments the thickness can be between 5 to 10 nm, and in yet otherembodiments the thickness can be between 150 to 250 nm. As appreciatedby one of ordinary skill in the art having the benefit of thisdisclosure, the thickness of the second AlGaN layer 1705 can be set toany suitable value. Further, as appreciated by one of ordinary skill inthe art, the 2DEG charge density control technique described above canemploy one or more islands, different sizes and shapes for each island,non-uniform spacing between each island and other characteristics thatcan be different than those described herein. Moreover, as appreciatedby one of ordinary skill in the art, the P-type GaN layer can havevarying values of doping densities. Furthermore, the second AlGaN layer1705 may have varying concentrations of Al and GaN. Moreover, a thirdAlGaN layer can formed on the second AlGaN layer 1705 for controllingthe 2DEG charge density. In some embodiments, a plurality of AlGaNlayers can be used for the control of the 2DEG charge density.

FIG. 18 illustrates a cross-sectional view of a GaN device 1800according to an embodiment of the disclosure. As shown in FIG. 18 , GaNdevice 1800 can include a GaN layer 1804, a first AlGaN layer 1808 and a2DEG layer 1806 formed between the GaN layer 1804 and the first AlGaNlayer 1808. The GaN device 1800 can include isolation implanted regions1802. The GaN device 1800 can further include a second AlGaN layer 1805formed on the first AlGaN layer 1808. In the illustrated embodiment, thesecond AlGaN layer 1805 can be removed in some areas, such as in area1820. As discussed above, isolation implant regions 1802 can be utilizedin the GaN device 1800 where an isolation implant can be placed into theactive regions of the GaN device 1800. The isolation implanted regions1802 can produce damaged lattice structure in the underlying first AlGaNlayer 1808 and GaN layer 1804, eliminating charge carriers in the 2DEGlayer 1806. Further, the damaged lattice structures can reducepiezoelectric effects beyond the immediate implanted regions and cancause a reduction of charge carriers in the adjacent 2DEG regions. Theaddition of the second AlGaN layer 1805 on the first AlGaN layer 1808 inthe area 1822 can increase the charge density in the 2DEG layer 1806below the regions where the second AlGaN layer 1805 is present (forexample location 1818). As before, the presence of isolation implantedregions 1802 can eliminated the 2DEG charge density in those regions,for example, location 1812.

Similar to the discussion above in FIGS. 2A and 2B, the 2DEG chargecarriers can be eliminated where the isolation implanted regions 1802are present, where isolation implants used for forming the isolationimplanted regions 1802 can penetrate through the second AlGaN layer 1805and the first AlGaN layer 1808. In some embodiments, the isolationimplant may penetrate into the GaN layer 1804. The addition of thesecond AlGaN layer 1805 can increase the 2DEG charge density below theregions with the second AlGaN layer 1805. The amount of increase of 2DEGcharge density can depend on a thickness of the second AlGaN layer 1805.In some embodiments, the thickness of the second AlGaN layer 1805 canbe, for example, 50 nm. In various embodiments, the thickness of thesecond AlGaN layer 1805 can be, for example, 100 nm, while in otherembodiments the thickness can be between 5 to 10 nm, and in yet otherembodiments the thickness can be between 150 to 250 nm. As appreciatedby one of ordinary skill in the art having the benefit of thisdisclosure, the thickness of the second AlGaN layer 1805 can be set toany suitable value. Further, as appreciated by one of ordinary skill inthe art, the 2DEG charge density control technique described above canemploy one or more isolation implanted regions, different sizes andshapes for each isolation implanted region, non-uniform spacing betweeneach isolation implanted region and other characteristics that can bedifferent than those described herein. Moreover, as appreciated by oneof ordinary skill in the art, the isolation implanted regions can havevarying values of depths. Furthermore, the second AlGaN layer 1805 mayhave varying concentrations of Al and GaN. Moreover, a third AlGaN layercan be formed on the second AlGaN layer 1805 for controlling the 2DEGcharge density. In some embodiments, a plurality of AlGaN layers can beused for the control of the 2DEG charge density.

FIG. 19 illustrates a cross-sectional view of an embodiment of GaNdevice 1900 using isolation implanted regions through P-type GaNstructures with a second AlGaN layer, according to an embodiment of thedisclosure. As shown in FIG. 19 , GaN device 1900 can include a GaNlayer 1904, a first AlGaN layer 1908 and a 2DEG layer 1906 formedbetween the GaN layer 1904 and the first AlGaN layer 1908. The GaNdevice 1900 can include isolation implanted regions through P-type GaNstructures 1902. The GaN device 1900 can further include a second AlGaNlayer 1905 formed on the first AlGaN layer 1908. In the illustratedembodiment, the second AlGaN layer 1905 can be removed in some areas,such as in area 1920. Similar to the description above in FIGS. 3A and3B, isolation implanted regions though P-type GaN structures 1902 can beformed by implanting through the P-type GaN structures. The isolationimplanted regions through the P-type GaN structures 1902 can be utilizedin active regions of GaN device 1900 to reduce the charge density in the2DEG layer 1906. In the illustrated embodiment, due to presence ofP-type GaN structures, the isolation implant can penetrate less into thesubstrate, thus the produced lattice structure damage may not completelyeliminate the charge carriers in the 2DEG layer 1906. The addition ofthe second AlGaN layer 1905 on the first AlGaN layer 1908 in the area1922 can increase the charge density in the 2DEG layer 1906 below theregions where the second AlGaN layer 1905 is present (for examplelocation 1912).

The addition of the second AlGaN layer 1905 on the first AlGaN layer1908 can increase the 2DEG charge density below the regions with thesecond AlGaN layer 1905. The amount of increase of 2DEG charge densitycan depend on a thickness of the second AlGaN layer 1905. In someembodiments, the thickness of the second AlGaN layer 1905 can be, forexample, 50 nm. In various embodiments, the thickness of the secondAlGaN layer 1905 can be, for example, 100 nm, while in other embodimentsthe thickness can be between 5 to 10 nm, and in yet other embodimentsthe thickness can be between 150 to 250 nm. As appreciated by one ofordinary skill in the art having the benefit of this disclosure, thethickness of the second AlGaN layer 1905 can be set to any suitablevalue. Further, as appreciated by one of ordinary skill in the art, the2DEG charge density control technique described above can employ one ormore isolation implanted regions through P-type GaN regions, differentsizes and shapes for each region, non-uniform spacing between eachregion and other characteristics that can be different than thosedescribed herein. Moreover, as appreciated by one of ordinary skill inthe art, the isolation implanted regions through P-type GaN regions canhave varying values of depths. Furthermore, the second AlGaN layer 1905may have varying concentrations of Al and GaN. Moreover, a third AlGaNlayer can be formed on the second AlGaN layer 1905 for controlling the2DEG charge density. In some embodiments, a plurality of AlGaN layerscan be used for the control of the 2DEG charge density.

Although 2DEG charge control structures for GaN devices are describedand illustrated herein with respect to one particular configuration ofGaN device, embodiments of the disclosure are suitable for use withother configurations of GaN devices and non-GaN devices. For example,any semiconductor device can be used with embodiments of the disclosure.In some instances, embodiments of the disclosure are particularly wellsuited for use with silicon and other compound semiconductor devices.

For simplicity, various internal components, such as the details of thesubstrate, various dielectric and metal layers, contacts, othercomponents of GaN transistor 100 (see FIG. 1 ) are not shown in thefigures.

In the foregoing specification, embodiments of the disclosure have beendescribed with reference to numerous specific details that can vary fromimplementation to implementation. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense. The sole and exclusive indicator of the scope of the disclosure,and what is intended by the applicants to be the scope of thedisclosure, is the literal and equivalent scope of the set of claimsthat issue from this application, in the specific form in which suchclaims issue, including any subsequent correction. The specific detailsof particular embodiments can be combined in any suitable manner withoutdeparting from the spirit and scope of embodiments of the disclosure.

Additionally, spatially relative terms, such as “bottom or “top” and thelike can be used to describe an element and/or feature's relationship toanother element(s) and/or feature(s) as, for example, illustrated in thefigures. It will be understood that the spatially relative terms areintended to encompass different orientations of the device in use and/oroperation in addition to the orientation depicted in the figures. Forexample, if the device in the figures is turned over, elements describedas a “bottom” surface can then be oriented “above” other elements orfeatures. The device can be otherwise oriented (e.g., rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein interpreted accordingly.

Terms “and,” “or,” and “an/or,” as used herein, may include a variety ofmeanings that also is expected to depend at least in part upon thecontext in which such terms are used. Typically, “or” if used toassociate a list, such as A, B, or C, is intended to mean A, B, and C,here used in the inclusive sense, as well as A, B, or C, here used inthe exclusive sense. In addition, the term “one or more” as used hereinmay be used to describe any feature, structure, or characteristic in thesingular or may be used to describe some combination of features,structures, or characteristics. However, it should be noted that this ismerely an illustrative example and claimed subject matter is not limitedto this example. Furthermore, the term “at least one of” if used toassociate a list, such as A, B, or C, can be interpreted to mean anycombination of A, B, and/or C, such as A, B, C, AB, AC, BC, AA, AAB,ABC, AABBCCC, etc.

Reference throughout this specification to “one example,” “an example,”“certain examples,” or “exemplary implementation” means that aparticular feature, structure, or characteristic described in connectionwith the feature and/or example may be included in at least one featureand/or example of claimed subject matter. Thus, the appearances of thephrase “in one example,” “an example,” “in certain examples,” “incertain implementations,” or other like phrases in various placesthroughout this specification are not necessarily all referring to thesame feature, example, and/or limitation. Furthermore, the particularfeatures, structures, or characteristics may be combined in one or moreexamples and/or features.

In the preceding detailed description, numerous specific details havebeen set forth to provide a thorough understanding of claimed subjectmatter. However, it will be understood by those skilled in the art thatclaimed subject matter may be practiced without these specific details.In other instances, methods and apparatuses that would be known by oneof ordinary skill have not been described in detail so as not to obscureclaimed subject matter. Therefore, it is intended that claimed subjectmatter not be limited to the particular examples disclosed, but thatsuch claimed subject matter may also include all aspects falling withinthe scope of appended claims, and equivalents thereof.

What is claimed is:
 1. A gallium nitride (GaN) device comprising: acompound semiconductor substrate; a source region formed in the compoundsemiconductor substrate; a drain region formed in the compoundsemiconductor substrate and separated from the source region; atwo-dimensional electron gas (2DEG) layer formed in the compoundsemiconductor substrate and extending between the source region and thedrain region; a gate region formed on the compound semiconductorsubstrate and positioned between the source region and the drain region;and a plurality of isolated charge control structures disposed betweenthe gate region and the drain region.
 2. The GaN device of claim 1,wherein each of the plurality of isolated charge control structures arearranged to selectively reduce a charge density in the 2DEG layer undereach of the plurality of isolated charge control structures.
 3. The GaNdevice of claim 1, wherein each of the plurality of isolated chargecontrol structures is disposed on the compound semiconductor substrate.4. The GaN device of claim 3, wherein each of the plurality of isolatedcharge control structures comprises a GaN layer.
 5. The GaN device ofclaim 4, wherein the GaN layer comprises a P-type GaN layer.
 6. The GaNdevice of claim 1, wherein each of the plurality of isolated chargecontrol structures is disposed within the compound semiconductorsubstrate.
 7. The GaN device of claim 6, wherein each of the pluralityof isolated charge control structures comprises an isolation implantedregion.
 8. The GaN device of claim 5, wherein each of the plurality ofisolated charge control structures comprises an isolation implantedregion formed through the P-type GaN layer.
 9. The GaN device of claim1, wherein each of the plurality of isolated charge control structuresare formed in shape of an island.
 10. The GaN device of claim 1, whereinthe plurality of isolated charge control structures are disposedproximal to the gate region.
 11. The GaN device of claim 10, wherein theplurality of isolated charge control structures are arranged to reducean electric field proximal to the gate region.
 12. The GaN device ofclaim 9, wherein a pattern density of the plurality of isolated chargecontrol structures is constant in regions proximal to the gate regionand regions proximal to the drain region.
 13. The GaN device of claim 1,wherein each of the plurality of isolated charge control structures areformed in shape of a trapezoid extending from the gate region towardsthe drain region.
 14. The GaN device of claim 4, wherein each of theplurality of isolated charge control structures are formed in shape ofan ellipse extending from the gate region towards the drain region. 15.A method of controlling a charge density in a two-dimensional electrongas (2DEG) layer in a gallium nitride (GaN) device, the methodcomprising: providing a compound semiconductor substrate comprising afirst layer and a second layer, and further comprising a 2DEG layerformed between the first layer and the second layer; forming an activeregion; forming a gate region on the compound semiconductor substrateand across the active region; and forming a plurality of isolated chargecontrol structures on the active region, wherein each of the pluralityof isolated charge control structures are arranged to selectively reducea charge density in the 2DEG layer under each of the plurality ofisolated charge control structures.
 16. The method of claim 15, whereineach of the plurality of isolated charge control structures comprises aP-type GaN layer.
 17. The method of claim 15, wherein each of theplurality of isolated charge control structures comprises an isolationimplanted region.
 18. A gallium nitride (GaN) device comprising: acompound semiconductor substrate; a two-dimensional electron gas (2DEG)layer formed in the compound semiconductor substrate; a resistor formedin the compound semiconductor substrate, the resistor comprising anactive region, and a first and second ohmic contacts; and a plurality ofisolated charge control structures formed on at least a portion of theactive region, wherein each of the plurality of isolated charge controlstructures is arranged to reduce a charge density in the 2DEG layerunder each of the plurality of isolated charge control structuresthereby causing an increase in a resistance of the resistor.
 19. The GaNdevice of claim 18, wherein each of the plurality of isolated chargecontrol structures comprises a P-type GaN layer.
 20. The GaN device ofclaim 18, wherein a spacing between each adjacent charge controlstructure is lower than a minimum manufacturing width for the activeregion.